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authorJann Horn <jannh@google.com>2017-12-18 20:11:59 -0800
committerDaniel Borkmann <daniel@iogearbox.net>2017-12-21 02:15:41 +0100
commit179d1c5602997fef5a940c6ddcf31212cbfebd14 (patch)
tree67a91e768530270c4ba22747afde33fc23b40cf1 /kernel
parenta5ec6ae161d72f01411169a938fa5f8baea16e8f (diff)
downloadblackbird-obmc-linux-179d1c5602997fef5a940c6ddcf31212cbfebd14.tar.gz
blackbird-obmc-linux-179d1c5602997fef5a940c6ddcf31212cbfebd14.zip
bpf: don't prune branches when a scalar is replaced with a pointer
This could be made safe by passing through a reference to env and checking for env->allow_ptr_leaks, but it would only work one way and is probably not worth the hassle - not doing it will not directly lead to program rejection. Fixes: f1174f77b50c ("bpf/verifier: rework value tracking") Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/bpf/verifier.c15
1 files changed, 7 insertions, 8 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 102c519836f6..982bd9ec721a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3467,15 +3467,14 @@ static bool regsafe(struct bpf_reg_state *rold, struct bpf_reg_state *rcur,
return range_within(rold, rcur) &&
tnum_in(rold->var_off, rcur->var_off);
} else {
- /* if we knew anything about the old value, we're not
- * equal, because we can't know anything about the
- * scalar value of the pointer in the new value.
+ /* We're trying to use a pointer in place of a scalar.
+ * Even if the scalar was unbounded, this could lead to
+ * pointer leaks because scalars are allowed to leak
+ * while pointers are not. We could make this safe in
+ * special cases if root is calling us, but it's
+ * probably not worth the hassle.
*/
- return rold->umin_value == 0 &&
- rold->umax_value == U64_MAX &&
- rold->smin_value == S64_MIN &&
- rold->smax_value == S64_MAX &&
- tnum_is_unknown(rold->var_off);
+ return false;
}
case PTR_TO_MAP_VALUE:
/* If the new min/max/var_off satisfy the old ones and
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